The physiological characteristics of ear 3 leaf of N-efficient maize were studied under the condition of high-N and low-N. The results showed that the ear leaf of N-efficient maize varieties had stable chlorophyll SPAD value under both high-N and low-N conditions, which extended and stabilized the duration of peak photosynthetic efficiency. The nitrate nitrogen content and nitrate reductase activity of ear 3 leaf were superior to those of the low efficiency cultivars. Therefore, N-efficient varieties have certain adaptability in high-N and low-N soil environment,and ear 3 leaf has higher nitrogen accumulation and utilization ability, which can effectively promote the improvement of nitrogen efficiency.